Several types of spear guns are known for use underwater and may generally be categorized by the type of propulsion employed for the spear. A first type of gun uses one or more elastic cords fixed near the tip of the gun. A spear is mounted on the gun and the cords are stretched and hooked to the spear. When the spear is released, the elastic cords rapidly contract, thereby propelling the spear. Spear guns of the type just described are disclosed, for example, in U.S. Pat. Nos. 3,585,979 and 4,193,386.
Although the elastic cord type of spear gun is very popular because of its simplicity, such spear guns suffer several significant disadvantages. The elastic cords degrade quickly when exposed to sun and salt water, the two elements in which the guns are commonly used. When the cords fail, it is most often while the gun is in use, making repair inconvenient and time consuming. Also, when the elastic cords are stretched and hooked to the spear, the cords quickly lose their tendency to return to their relaxed position. Consequently, some of the energy used to stretch the cords is lost before the spear is released. Another disadvantage associated with the elastic cord type of spear gun is that the gun usually is cocked, that is, the elastic cords stretched and hooked to the spear, while the user is in the water, a difficult and potentially dangerous procedure. Further, since the elasticity of the cords determines the range and effectiveness of the gun, guns with greater range and power require corresponding greater cocking efforts and thus are even more difficult and dangerous to use.
Yet another disadvantage of the elastic cord spear guns is that the trigger mechanism must hold the entire force of the elastic cords once the gun is cocked and then release the spear when the trigger is actuated. The large forces involved tend to quickly wear the trigger mechanism, requiring frequent service which, if not performed, can lead to an unsafe gun.
A second general type of spear gun is an air powered gun which uses compressed air to force a piston down a smooth barrel. A spear resting within the barrel is propelled by the piston as the piston travels down the barrel. The air which drives the piston may come from two sources, namely, from a cylinder of compressed air, known as "cylinder charged," or by forcing the piston back down the barrel and capturing the resulting compressed air, known as "compression charged." Cylinder charged guns may have considerable power and range but the large volume of air used with each firing of the gun requires an air cylinder that is large and difficult to handle. An example of the cylinder charged gun is disclosed in U.S. Pat. No. 4,019,480.
The compression charged gun is more popular than the cylinder charged gun and is often comparable in weight to elastic cord guns. Unfortunately, the effort required to recompress the air within the barrel is considerable and, as with the elastic cord guns, the cocking operation can be difficult and perhaps dangerous. A disadvantage common to both types of compressed air guns is that the piston requires an air seal that can move rapidly down the barrel. Such a seal is difficult to maintain, particularly in view of the speed at which the piston must move and the salt water and sand environment in which the guns operate. Consequently, both types of compressed air spear guns suffer from frequent seal failures.
Applicant is aware of a spear gun which uses a conventional .38 caliber firearm cartridge to propel a spear from the gun. The gun bears the legend "Mordem Brevettato, Italy" and it is believed that the gun was made in Italy during the late 1940's. The gun includes a spear that is loosely received within a barrel. The end of the spear that is received within the barrel includes an indentation that is adapted to receive the cartridge and in particular the projectile when the cartridge is fired. The Mordem gun, however, is ineffective and of little practical use. Because such gun uses a conventional firearm cartridge, the cartridge can become flooded with water, rendering the cartridge, and thus the gun, inoperative. If the cartridge does fire, the projectile is rammed into the indentation in the spear, transferring the momentum of the projectile to the spear. However, the mass of the spear is so much greater than the projectile that little force is actually transferred to the spear. Moreover, due to the loose fit of the spear within the barrel, expanding gas from the the cartridge largely blows ineffectively around and by the spear. The net result is that the spear is not propelled from the gun with any appreciable speed. Applicant believes that the Mordem gun was a commercial failure at least because of the low power associated therewith.
It is known in the art to use conventional firearm cartridges in what are often termed "power heads," that is, devices carried at the tip of spears which, upon impact with a target, cause the cartridge to detonate, propelling a dart or projectile into the target. Such devices are disclosed in U.S. Pat. Nos. 3,838,532 (Prodanovich) and 3,871,120 (Mounier). Prodanovich discloses the use of a conventional .22 caliber cartridge to propel a dart into the target upon inpact of the dart with the target. As an alternative, the dart may be dispensed with and the expanding gases and projectile from the cartridge can be used to immobilize smaller marine creatures. Mounier discloses an impact-activated underwater gun which uses a firearm cartridge including a projectile.
Both the Prodanovich and Mounier power heads are contact devices truly effective only when the devices contact or are in very close proximity with a target. With respect to Prodanovich, the force of impact of the projectile from the cartridge can damage the dart and the barrel within which the dart travels, an important disadvantage where long life and dependable service are needed.
Also known in the art are so-called "bang sticks" used to repell sharks and the like. Some of such bang sticks use a small waterproof shotgun-like cartridge mounted at the front of the stick. The cartridge is fired when the stick is directed so as to strike a shark, expelling pellets and a burst of expanding gases against the shark. However, as with power heads, bang sticks are only effective when in close proximity with a target.